1. Field of the Invention
This invention relates to a method for manufacturing a flat display panel device suitable for being applied to a plasma display panel and the like. More specifically, the invention relates to a method wherein, when at least barrier ridges are formed by a jet treatment using an abrasive (sandblast), damages of a substrate and/or electrodes formed on the substrate are reduced as much as possible by using organic material particles coated with an inorganic material as the abrasive, so that improvement in variations in luminous brightness and the like can be attained.
2. Description of the Prior Art
Hitherto, as a display device for displaying images, various types have been suggested, such as a CRT display device or a liquid crystal device. In recent years, highly minute display methods such as HDTV (High Definition TV) have been made practicable. Following this, display devices are becoming large-sized and highly minute.
The CRT display device and the like have such a problem that they cannot be structurally adapted to the advance toward large-sized devices. Further, the liquid display device, which is spotlighted as a flat display panel device, also has problems that high luminous brightness cannot be obtained and its structure is complicated, and that it is difficult that the device is made large-sized, except for a projection type device.
On the other hand, in a plasma display device (plasma display panel) (PDP)) using plasma, a high luminous brightness can be obtained, although its structure is relatively simple. Besides, it can be made large-sized. Thus, in recent years, it has greatly been demanded to make the PDP practicable as a flat display panel.
As is well known, the PDP device comprises two glass substrates, pattern electrodes arranged in a very small space formed by barrier ridges between the two glass substrates and fluorescent substance layers (R, G and B) formed in the spaces so as to cover the surfaces of electrodes wherein discharge gas is injected into the spaces, this space is formed as a cell (pixel), and a large number of the same cells are arranged in a matrix form.
FIG. 1 is a cross sectional view showing essential parts of an example of a color PDP device 10. The device shown in this figure is a color PDP device driving cells in an alternating current system.
The PDP device 10 is composed of a back side section 10A, a front side section 10B, and an image display section (display cell) 20 arranged between them. The back side section 10A is provided with a glass substrate 12 having predetermined thickness and size. Address electrodes 14 (14R, 14G and 14B) are adhered to the surface of the glass substrate 12 with keeping a given interval between them.
In the intermediate portions between the address electrodes 14, barrier ridges 16 having predetermined height and width are formed in parallel to the address electrodes 14. In this example, inside very small spaces (display cells) 20 (20R, 20G and 20B) put between these barrier ridges 16, three different sorts of the fluorescent substances 18 are alternately formed at predetermined repeated pitches, so as to cover the address electrodes 14. Each of said fluorescent substances 18 (18R, 18G and 18B) emits a fluorescent color light of a red (R), a green (G), or a blue (B).
The front side section 10B opposite to the back side section 10A also has a glass substrate 22 for the front side. As also shown in FIGS. 1 and 2, display electrodes 24, which are transparent electrodes, are arranged on the lower surface side of the glass substrate 22 and formed at given intervals along the direction perpendicular to the address electrodes 14. Furthermore, display electrodes 26 for bus lines, which are narrower than the display electrodes 24, are formed on the upper surface side of the display electrodes 24. A protective layer (for example, MgO) 28 is deposited on the electrodes 24 and 26 so that said layer 28 may cover the whole of these electrodes 24 and 26.
The front side section 10B is sealed in a state that its protective layer 28 contacts the barrier ridges 16, and thus, the section 10B is integrated with the back side section 10A. Thereby, the PDP device is formed. The respective display cells 20 are filled with discharge gas. By electric discharge between the opposite electrodes in the respective display cells, the discharge gas is excited. By ultraviolet rays generated when the excited discharged gas returns to the ground state, the fluorescent substances 18 emit light, causing luminescence of the display cells (pixels).
Incidentally, the barrier ridges 16 formed between the aforementioned display cells are produced as follows. It is explained referring to FIG. 3.
First, glass particles are dispersed into a binder and thus, an inorganic paste is formed. As shown in FIG. 3, the inorganic paste is applied into a multilayer form by a screen print method over the whole surface of the glass substrate 12 having thereon the formed address electrodes 14, so as to form a barrier-ridge-forming layer (inorganic material layer) 16a having a certain film thickness. Thereafter, a mask 30a corresponding to the discharge space areas (cell areas) is made on the barrier-ridge-forming layer 16a, and then the exposed portions of the barrier-ridge-forming layer 16a are removed off by jet treatment. As shown in FIG. 1, by this treatment, unnecessary portions for the discharge space areas are removed from the barrier-ridge-forming layer 16a to form barrier ridges 16 having predetermined width and height.
Referring to FIG. 4, a method for forming the fluorescent substance layers 18 inside the discharge spaces having the exposed electrodes 14 will be explained. As shown in the FIG.4, after filling the discharge spaces with a fluorescent paste 21 and drying the paste, the fluorescent substance layer 21 is removed by jet treatment up to a given thickness as shown by the dotted line of FIG. 4. The layer is actually removed up to such a thickness that the plasma discharge spaces can be kept. Through this treatment, the display cells 20 (29R, 20G and 20B) are formed.
It is well known that particles with a large Mohs hardness such as calcium carbonate are used as the abrasive for the aforementioned jet treatment. However, it was proved that the surface of the glass substrate 12 or those of the address electrodes 14 formed on the glass substrate 12 were liable to be damaged by the jet treatment with an abrasive, in particular in the process for forming the barrier ridges 16 as shown in FIG. 3 because the abrasive was composed of angular particles as shown in FIG. 5. FIG. 6(A) shows results of measuring the surface roughness of the glass substrate 12 before the jet treatment. The measured results indicated that the surface was flat.
On the other hand, FIG. 6(B) shows results of measuring the surface roughness of the exposed glass substrate 12 having been subjected to the aforementioned jet treatment. The measured results indicated that the surface was damaged by the abrasive, as shown in the curve Pa of FIG. 6 (B) and consequently the surface became depressed.
Further, FIG. 7 shows an example of the particle size distribution of calcium carbonate used as the abrasive in the above case. The average particle size in the FIG. 7 is 19 .mu.m, but fine particles having a particle size of 1 .mu.m or less are considerably contained therein. Namely, when the accumulated amount of particles passed "through the sieve" is expressed by %, the percentage is shown by the curve La in FIG. 7. This curve La indicates the percentage (%) of particles having a certain particle size or less in the whole. From the example shown in FIG. 7, it can be understood that particles having a particle size of, for example, 1 .mu.m or less account for about 20% of the whole particles.
When fine particles are numerous in the abrasive as described above, the fine particles are liable to adhere to the surface of the glass substrate 12 or those of the address electrodes 14. Since such the fine particles cannot be removed in subsequent steps, they remain on the surface as they are. As a result, surface roughness deteriorates. For example, the curve Pb shown in FIG. 6(B) indicates that the fine particles (particles of several .mu.m or less size) in the abrasive adhere to the surface of the glass substrate 12.
Not only the surface of the glass substrate 12 but also those of the address electrodes 14 formed on the substrate 12 are subjected to the surface damage with the abrasive and the adhesion of the fine particles.
Where particles made of calcium carbonate or the like are used as the abrasive, not only the surface of the glass substrate but also those of the address electrodes 14 are liable to be damaged. In the case of FIG. 4, it is feared that said particles also damage the surface of the fluorescent substance layers removed unnecessary portions therefrom harder than required. Thus, luminous brightness is easily varied and operation voltage is also varied with ease. There is a drawback that any PDP device having a high quality cannot be obtained.
It has been investigated that as the abrasive other than calcium carbonate are used the materials which can be gasified by heating or burning, such as ethylcellulose particles or carbon particles (for example, Japanese Unexamined Patent Application publication No.101777/Heisei 4).
As for the abrasive described in this publication, particles thereof are liable to adhere to the processed face of glass substrate 12 or those of the address electrodes 14. It is difficult to uniformly process the surface with the particles and thus, resulting in a problem about processing quality. Therefore, said particles are not practical as the abrasive.
Alternatively, as abrasives other than these, silicon carbide, alumina, a glass bead and the like are used. As regards hardness thereof (Mohs), however, they have Mohs' hardness of 13, 12 and 6, respectively. Therefore, it is feared that any one of them injures the glass substrate (Mohs' hardness: 6) and the address electrodes (Mohs' hardness: 4).